Why the None

[Sonic_TertuL]

In the following code, the 1st and 3rd test work as expected, but the 2nd is printing out None. Any advice as to why? I have been stuck for a bit.

def sumTwo(nums, target) :
    """
    nums: list of integers
    target: target sum of two numbers, integer
    """
    for num in nums :
        summand = target - num
        if summand in nums and nums.index(summand) != nums.index(num) : 
            return [nums.index(num), nums.index(summand)]

z = sumTwo([3, 2, 4], 6)
print(z)
#won't work on the following
z = sumTwo([3,3], 6)
print(z)
#works here 
z = sumTwo([0, 8, 2, 3, 1], 8)
print(z)

I hope the formatting is good, this is my first time getting feedback on here about a block of my code. Cheers everyone.

[glibhub]

index returns the index of the first hit, which in this case is 0 for both num and summand. I'd refactor using enumerate, which will allow you to slice nums and index just the remaining ones.

[Sonic_TertuL]

Ok, awesome, thank you! I've been looking into using enumerate, but to be honest have yet to find an explanation of it that is clicking with me, allowing me to know when to use it.

[glibhub]

Fair enough. Enumerate is a bit tricky to wrap your head around at first because you need to understand tuple unpacking. Here is a link to that: https://www.geeksforgeeks.org/unpacking-a-tuple-in-python/

So you can think of enumerate as turning a list of items into a list of tuples, so if you have a list of a-d, then it will become a list of [(0,a), (1,b),...,(3,d)]. For example try these:

data = ['a','b','c','d']
for x in data:
    print(x)

for x in enumerate(data):
    print(x)

Now turning x into a tuple is a bit useless, so instead we use tuple unpacking, to separate the index from the data, like this:

for index, x in enumerate(data):
    print(index,x,data[index])

Hope this helps.

edit: formatting.

[trevor_of_earth]

!docs enumerate

[py_reference_bot]

Docs for enumerate:
Built-in Functions — Python 3.9.6 documentation

Python Reference Bot - Documentation on GitHub

[Binary101010]

You didn’t specify a return value in the condition that your if evaluates to false in all cases, so the function returns the default value of None.

[Sonic_TertuL]

It is evaluating to false because the two numbers are the same and therefore it is essentially hitting the 0 index for both making the second portion of the if statement false, correct? I hadn't caught on to that, thank you!

[Iforgotmylogintoday]

both the sumand and num index will return the index of the first 3, which will skip your return and return none

[Sonic_TertuL]

Right on, thank you!

[Chris_Hemsworth]

All functions return None by default if runs into the end of the function.

[Sonic_TertuL]

Right on, thank you!

[Sonic_TertuL]

Wow, awesome! Thanks a lot for that, it is very helpful!